This invention contains environmentally clean engine designs that emit zero or very low pollutant levels during operation. The CLEAN AIR ENGINE (CLAIRE) invention is directly applicable to both transportation type vehicles including automobiles, trucks, trains, airplanes, ships and to stationary power generation applications. The designs feature hybrid, dual cycle and single cycle engines. More specifically, this invention relates to low or no pollution generating hydrocarbon combustion based power generation systems which isolates and conditions carbon dioxide (CO2) generated in the system for injection and sequestering into terrestrial formations such as underground geological formations and oceans.
The current art in generating power for transportation purposes basically utilize the internal combustion gas or diesel engine. The current art for electric power generation utilize gas turbines and/or steam turbines. These devices burn hydrocarbon fuels with air which contains (by weight) 23.1% oxygen, 75.6% nitrogen and the remaining 1.3% in other gases. The emissions resulting from the combustion of fuels for internal combustion engines (gasoline or diesel), with air contain the following pollutants that are considered damaging to our air environment. These smog causing pollutants, are: total organic gases (TOG); reactive organic gases (ROG); carbon monoxide (CO); oxides of nitrogen (NOx); oxides of sulfur (SOx); and particulate matter (PM). Approximately one half of the total pollutants emitted by all sources of air pollution in California are generated by road vehicles (Emission Inventory 1991, State of California Air Resources Board, prepared January 1994). The major source of this vehicle pollution comes from passenger cars and light to medium duty trucks.
No near term solutions appear in sight to drastically reduce the vast amount of air pollutants emitted by the many millions of automobiles and trucks operating today. Based on the State of California Air Resources Board study, the average discharge per person in California of the air pollutants from mobile vehicles, monitored by this agency during 1991 and reported in 1994, was approximately 1.50 lb/day per person. With a nationwide population of over 250,000,000 people, this data extrapolates to over 180,000 tons of air borne emissions per day being discharged in the USA by mobile vehicles. Also, the number of cars and miles that are being driven continue to increase, further hampering efforts to reduce smog causing pollutants.
Allowable emission thresholds are rapidly tightening by Federal and State mandates. These allowable emission reductions are placing severe demands on the transportation industry and the electric power generating industry to develop new and lower emission power systems.
Although considerable effort is being directed at improving the range of electric zero emission vehicles (ZEV) by developing higher energy capacity, lower cost storage batteries, the emission problem is been transferred from the vehicle to the electric power generating plant, which is also being Federally mandated (Clean Air Act Amendments of 1990) to reduce the same air toxic emissions as those specified for automobiles and trucks.
The current world wide art of generating power for consumers of electricity depends primarily on fossil fuel burning engines. These engines burn hydrocarbon fuels with air. As described above, combustion of fossil fuels with air usually produce combustion products that contain a number of pollutants. Current Unites States regulatory requirements prescribe the amounts of the atmospheric pollutants permitted in particular locations. Allowable pollutant thresholds are decreasing over time and thereby putting more and more pressure on industry to find better solutions to reduce these emissions of pollutants in the electric power generating industry and other power generating industries.
Other energy sources being developed to solve the emissions problem, by exploiting non combustible energy sources include fuel cells and solar cells. Developers are solving many of the technological and economic problems of these alternate sources. However, widespread use of these energy sources for vehicles and for electric power generating facilities do not appear to yet be practical.
In addition to the emission of pollutants, combustion based power generation systems also generate significant amounts of carbon dioxide (CO2). While CO2 emissions are currently not regulated in the United States, concern has been voiced by experts over the release of CO2 and other greenhouse gases into the environment. One method for eliminating the formation of CO2 in combustion based power generation systems is to utilize hydrogen as the fuel rather than a hydrocarbon fuel. Use of hydrogen as a fuel has many drawbacks including the highly flammable and potentially explosive nature of hydrogen when in a gaseous state, the significant energy required to maintain hydrogen in a liquid state, the low density of hydrogen requiring large volumetric storage capacity and the fact that all present commercial production of hydrogen comes from fossil fuels which also yield CO2 as a by-product.
Some attention has recently been given to the concept of separating the CO2 from other combustion products and then disposing of the CO2 by injecting it into deep porous geological formations or deep into the earth""s oceans where environmental impacts of the release of the CO2 would be minimized. Interest in such terrestrial formation disposal techniques is exemplified by the recent issuance by the United States Department of Energy of a Small Business Innovation Research (SBIR) program solicitation (reference number DOE/ER-0706, closing date Mar. 2, 1998) specifically seeking strategies for mitigation of greenhouse gases and pollutants including CO2. This solicitation sought approaches to CO2 disposal involving usage of potential storage sites such as oil and gas reservoirs, unmineable coal seams, the deep ocean, or deep confined aquifers. CO2 separation and injection systems are known in the prior art but the CO2 is only partially separated and the processes are so energy intensive that such systems are not generally commercially viable. Accordingly, a need exists for such a more efficient CO2 separation and injection system which can sequester and dispose of the CO2 in an economically viable manner.
This invention provides a means for developing a zero or very low pollution vehicle (ZPV) and other transportation power systems (i.e. rail and ship), as well as a zero or low pollution electric power generating facility. The zero or very low pollution is achieved by removing the harmful pollutants from the incoming fuel and oxidizer reactants prior to mixing and burning them in a gas generator or combustion chamber. Sulfur, sulfides and nitrogen are major pollutants that must be removed from the candidate fuels: hydrogen, methane, propane, purified natural gas, and light alcohols such as ethanol and methanol. Since air contains 76% nitrogen by weight, it becomes a major source of pollution that also requires removal prior to combining it with the clean fuel.
Cleansing of the fuel is straightforward and requires no further elaboration. The separation of the oxygen from the nitrogen in the air, however, is accomplished in a variety of ways. For instance, nitrogen can be removed from air by the liquefaction of air and gradual separation of the two major constituents, oxygen and nitrogen, by means of a rectifier (to be described later in more detail). The separation of the gases relies on the two distinct boiling points for oxygen (162xc2x0 R) and for nitrogen (139xc2x0 R) at atmospheric pressure. Air liquefies at an intermediate temperature of (142xc2x0 R).
Other nitrogen removal techniques include vapor pressure swing adsorption, and membrane based air separation. With vapor pressure swing adsorption, materials are used which are capable of adsorption and desorption of oxygen. With membrane based air separation, an air feed stream under pressure is passed over a membrane. The membrane allows one component of the air to pass more rapidly there through than other components, enriching the amount of different components on opposite sides of the membrane. Such membranes can be of a variety of different materials and use several different physical processes to achieve the desired separation of nitrogen out of the air.
One embodiment of this invention consists of a hybrid power system that combines a Rankine cycle thermal cycle with an auxiliary electric motor for start-up and chill-down requirements. The thermal power cycle of the engine begins by compressing ambient air to high pressures, cooling the air during compression and during the expansion to liquid air temperatures in a rectifier where separation of the oxygen and nitrogen takes place. The cold gaseous nitrogen generated is used to cool the incoming air and then is discharged to the atmosphere at near ambient temperature. Simultaneously, the cold gaseous or liquid oxygen generated by the rectifier is pressurized to gas generator pressure levels and delivered to the gas generator at near ambient temperature. Fuel, gaseous or liquid, from a supply tank is pressurized to the pressure level of the oxygen and also delivered to the gas generator where the two reactants are combined at substantially the stoichiometric mixture ratio to achieve complete combustion and maximum temperature hot gases (6500xc2x0 R). These hot gases are then diluted with water downstream in a mixing section of the gas generator until the resulting temperature is lowered to acceptable turbine inlet temperatures (2000xc2x0 R).
The drive gas generated from this mixing process consists of high purity steam, when using oxygen and hydrogen as the fuel, or a combination of high purity steam and carbon dioxide (CO2), when using oxygen and light hydrocarbon fuels (methane, propane, methanol, etc.). Following the expansion of the hot gas in the turbine, which powers the vehicle or the electric power generating plant, the steam or steam plus CO2 mixture are cooled in a condenser to near or below atmospheric pressure where the steam condenses into water, thus completing a Rankine cycle. Approximately 75% of the condensed water is recirculated to the gas generator while the remainder is used for cooling and discharged to the atmosphere as warm water vapor. When using light hydrocarbons as the fuel, the gaseous carbon dioxide remaining in the condenser is compressed to slightly above atmospheric pressure and either converted to a solid or liquid state for periodic removal, or the gas can be discharged into the atmosphere when such discharge is considered non-harmful to the local air environment.
Since this thermal cycle requires time to cool the liquefaction equipment to steady state low temperatures, an electric motor, driven by an auxiliary battery, can be used to power the vehicle and initiate the Rankine cycle until chill-down of the liquefaction equipment is achieved. When chill-down is complete the thermal Rankine engine, connected to an alternator, is used to power the vehicle or stationary power plant and recharge the auxiliary battery.
The combination of these two power systems, also referred to as a hybrid vehicle, emit zero or very low pollution in either mode of operation. In addition, the electric motor battery is charged by the zero or very low pollution thermal Rankine cycle engine itself and thus does not require a separate electric power generating plant for recharge. This reduces the power demand from central power stations and also reduces a potential source of toxic air emissions.
In place of the electric drive motor and battery, the Rankine cycle engine, with the addition of a few control valves, can also be operated as a minimally polluting open Brayton cycle, burning fuel and incoming air to power the vehicle during the period necessary to allow the Rankine cycle engine liquefaction equipment time to chill-down. This feature is another embodiment of this invention.
The zero or very low pollution Rankine cycle engine can also be used in a single cycle thermal mode for vehicles with long duration continuous duty such as heavy trucks, trains, ships and for stationary power generation plants where the chill-down time is not critical to the overall operational cycle.
The adaptation of the Otto and Diesel thermal cycles to a low-polluting hybrid engine are also included as embodiments of this invention. By using these thermal cycles, the need for a condenser and recirculating water system are eliminated. Low temperature steam or steam/carbon dioxide gases are recirculated as the working fluid and therefore replace the function of the recirculating water quench of the Rankine cycle embodiments previously discussed.
The combustion products resulting from operation of the above-described engine are substantially entirely H2O and CO2 (when a hydrocarbon fuel is used). These combustion products are in contrast to combustion products resulting from typical hydrocarbon combustion based power generation systems which do not have an air constituent separation device, as identified above. Combustion products in such prior art systems would also include a large amount of nitrogen and unused oxygen as well as NOx and various carbon containing species. Because the combustion products resulting from the above-described engine are merely H2O and CO2, the isolation and conditioning of CO2 is straight forward and draws little power away from the system as a whole.
Specifically, the combustion products are passed through a condenser where the H2O condenses into a liquid phase. Gases exiting the condenser are substantially only carbon dioxide and can be directed out of the condenser for use in a terrestrial formation injection system or other disposal, such as for use in industrial processes requiring CO2. To most effectively inject the CO2 into a deep terrestrial formation, the CO2 must be pressurized. Such formations include oceans; deep aquifers; and porous geological formations such as partially or fully depleted oil or gas formations, salt caverns, sulfur caverns and sulfur domes. To accomplish such pressurization the gaseous CO2 can be compressed in one or more stages with after cooling and condensation of additional water. The modestly pressurized CO2 can then be further dried by conventional methods such as through the use of molecular sieves and passed to a CO2 condenser where the CO2 is cooled and liquefied. The CO2 can then be efficiently pumped with minimum power to a pressure necessary to deliver the CO2 to a depth within the geological formation or the ocean depth at which CO2 injection is desired. Alternatively, the CO2 can be compressed through a series of stages and discharged as a super critical fluid at a pressure matching that necessary for injection into the geological formation or deep ocean.
Accordingly, a primary object of the present invention is to provide a low or zero pollution combustion based power generation system which additionally isolates and conditions CO2 from combustion products discharged by the system for effective handling of the CO2 in a manner other than release of the CO2 into the atmosphere.
Another object of this invention is to provide a high efficiency combustion based power generation system.
Another object of the present invention is to provide a power generation system which can also produce water as a byproduct. In areas where water is scarce the water byproducts produced by this invention are particularly beneficial.
Another object of the present invention is to provide a combustion based power generation system which includes an air treatment plant for separating nitrogen from the air prior to use of the air to combust a hydrocarbon fuel, such that nitrogen oxides and other pollutants are reduced or eliminated as byproducts of combustion in the power generation system.
Another object of the present invention is to provide a hydrocarbon combustion based power generation system which injects CO2 produced by the power generation system into a terrestrial formation such as a deep porous geological structure or an undersea location.
Another object of the present invention is to provide a combustion based power generation system which releases no combustion products into the atmosphere.
Another object of the present invention is to provide a reliable and economical source of power which does not harm the surrounding environment.
Other further objects of this invention will become apparent upon a careful reading of the included description of the invention and review of the drawings included herein, as well as the claims.